Eddie Jones has warned his England stars they must improve their fitness to become a dominant force in international rugby.
It has been a solid start to Jones' tenure as head coach with England winning their opening two Six Nations matches against Scotland and Italy.
However, the Australian believes his side have work to do to overcome their shortcomings and make the step up from club rugby.
"They're not right for international rugby, that's the distinction," Jones told BBC Radio 4.
"They're right for club rugby. They can play club rugby 365 days of the year but international rugby is faster, there's more accelerations, the running speed is higher and you need to have a different sort of training for international rugby.
"But we'll get it right in the future. It's quite simple to me that the time we have with them we work them hard, work them at the level we need to, and when they go away to their clubs if they need to do extra work they do it and if they don't do it then England won't be a dominant country."
Jones, who has worked in England before with Saracens, says he expects domestic teams to help the national side with their ambitions.
"They have to assist without a doubt and I've got no doubt English clubs will do that," he added.
"One of the things I've noticed since I've been back is how professional and how well structured the clubs are. They've got strength and conditioning staff and medical staff at rates nowhere else in the world have.
"You've got to remember they're coaching players to be successful at club level, they're not coaching their players to be successful at international level, which is 100 per cent right.
"We've got to get them to understand and the players to understand that, to be successful at international level, there's a plus factor there."